Pick up a research paper on battery technology, fuel cells, energy storage technologies or any of the advanced materials science used in these fields, and you will likely find somewhere in the introductory paragraphs a throwaway line about its application to the storage of renewable energy. Energy storage makes sense for enabling a transition away from fossil fuels to more intermittent sources like wind and solar, and the storage problem presents a meaningful challenge for chemists and materials scientists… Or does it?

Guest Post by John Morgan. John is Chief Scientist at a Sydney startup developing smart grid and grid scale energy storage technologies. He is Adjunct Professor in the School of Electrical and Computer Engineering at RMIT, holds a PhD in Physical Chemistry, and is an experienced industrial R&D leader. You can follow John on twitter at @JohnDPMorgan. First published in Chemistry in Australia.

Several recent analyses of the inputs to our energy systems indicate that, against expectations, energy storage cannot solve the problem of intermittency of wind or solar power. Not for reasons of technical performance, cost, or storage capacity, but for something more intractable: there is not enough surplus energy left over after construction of the generators and the storage system to power our present civilization.

The problem is analysed in an important paper by Weißbach et al.1 in terms of energy returned on energy invested, or EROEI – the ratio of the energy produced over the life of a power plant to the energy that was required to build it. It takes energy to make a power plant – to manufacture its components, mine the fuel, and so on. The power plant needs to make at least this much energy to break even. A break-even powerplant has an EROEI of 1. But such a plant would pointless, as there is no energy surplus to do the useful things we use energy for.

There is a minimum EROEI, greater than 1, that is required for an energy source to be able to run society. An energy system must produce a surplus large enough to sustain things like food production, hospitals, and universities to train the engineers to build the plant, transport, construction, and all the elements of the civilization in which it is embedded.

For countries like the US and Germany, Weißbach et al. estimate this minimum viable EROEI to be about 7. An energy source with lower EROEI cannot sustain a society at those levels of complexity, structured along similar lines. If we are to transform our energy system, in particular to one without climate impacts, we need to pay close attention to the EROEI of the end result.

The EROEI values for various electrical power plants are summarized in the figure. The fossil fuel power sources we’re most accustomed to have a high EROEI of about 30, well above the minimum requirement. Wind power at 16, and concentrating solar power (CSP, or solar thermal power) at 19, are lower, but the energy surplus is still sufficient, in principle, to sustain a developed industrial society. Biomass, and solar photovoltaic (at least in Germany), however, cannot. With an EROEI of only 3.9 and 3.5 respectively, these power sources cannot support with their energy alone both their own fabrication and the societal services we use energy for in a first world country.

Energy Returned on Invested, from Weißbach et al.,1 with and without energy storage (buffering). CCGT is closed-cycle gas turbine. PWR is a Pressurized Water (conventional nuclear) Reactor. Energy sources must exceed the “economic threshold”, of about 7, to yield the surplus energy required to support an OECD level society.

These EROEI values are for energy directly delivered (the “unbuffered” values in the figure). But things change if we need to store energy. If we were to store energy in, say, batteries, we must invest energy in mining the materials and manufacturing those batteries. So a larger energy investment is required, and the EROEI consequently drops.

Weißbach et al. calculated the EROEIs assuming pumped hydroelectric energy storage. This is the least energy intensive storage technology. The energy input is mostly earthmoving and construction. It’s a conservative basis for the calculation; chemical storage systems requiring large quantities of refined specialty materials would be much more energy intensive. Carbajales-Dale et al.2 cite data asserting batteries are about ten times more energy intensive than pumped hydro storage.

Adding storage greatly reduces the EROEI (the “buffered” values in the figure). Wind “firmed” with storage, with an EROEI of 3.9, joins solar PV and biomass as an unviable energy source. CSP becomes marginal (EROEI ~9) with pumped storage, so is probably not viable with molten salt thermal storage. The EROEI of solar PV with pumped hydro storage drops to 1.6, barely above breakeven, and with battery storage is likely in energy deficit.

This is a rather unsettling conclusion if we are looking to renewable energy for a transition to a low carbon energy system: we cannot use energy storage to overcome the variability of solar and wind power.

In particular, we can’t use batteries or chemical energy storage systems, as they would lead to much worse figures than those presented by Weißbach et al. Hydroelectricity is the only renewable power source that is unambiguously viable. However, hydroelectric capacity is not readily scaled up as it is restricted by suitable geography, a constraint that also applies to pumped hydro storage.

This particular study does not stand alone. Closer to home, Springer have just published a monograph, Energy in Australia,3 which contains an extended discussion of energy systems with a particular focus on EROEI analysis, and draws similar conclusions to Weißbach. Another study by a group at Stanford2 is more optimistic, ruling out storage for most forms of solar, but suggesting it is viable for wind. However, this viability is judged only on achieving an energy surplus (EROEI>1), not sustaining society (EROEI~7), and excludes the round trip energy losses in storage, finite cycle life, and the energetic cost of replacement of storage. Were these included, wind would certainly fall below the sustainability threshold.

It’s important to understand the nature of this EROEI limit. This is not a question of inadequate storage capacity – we can’t just buy or make more storage to make it work. It’s not a question of energy losses during charge and discharge, or the number of cycles a battery can deliver. We can’t look to new materials or technological advances, because the limits at the leading edge are those of earthmoving and civil engineering. The problem can’t be addressed through market support mechanisms, carbon pricing, or cost reductions. This is a fundamental energetic limit that will likely only shift if we find less materially intensive methods for dam construction.

This is not to say wind and solar have no role to play. They can expand within a fossil fuel system, reducing overall emissions. But without storage the amount we can integrate in the grid is greatly limited by the stochastically variable output. We could, perhaps, build out a generation of solar and wind and storage at high penetration. But we would be doing so on an endowment of fossil fuel net energy, which is not sustainable. Without storage, we could smooth out variability by building redundant generator capacity over large distances. But the additional infrastructure also forces the EROEI down to unviable levels. The best way to think about wind and solar is that they can reduce the emissions of fossil fuels, but they cannot eliminate them. They offer mitigation, but not replacement.

Nor is this to say there is no value in energy storage. Battery systems in electric vehicles clearly offer potential to reduce dependency on, and emissions from, oil (provided the energy is sourced from clean power). Rooftop solar power combined with four hours of battery storage can usefully timeshift peak electricity demand,3 reducing the need for peaking power plants and grid expansion. And battery technology advances make possible many of our recently indispensable consumer electronics. But what storage can’t do is enable significant replacement of fossil fuels by renewable energy.

If we want to cut emissions and replace fossil fuels, it can be done, and the solution is to be found in the upper right of the figure. France and Ontario, two modern, advanced societies, have all but eliminated fossil fuels from their electricity grids, which they have built from the high EROEI sources of hydroelectricity and nuclear power. Ontario in particular recently burnt its last tonne of coal, and each jurisdiction uses just a few percent of gas fired power. This is a proven path to a decarbonized electricity grid.

But the idea that advances in energy storage will enable renewable energy is a chimera – the Catch-22 is that in overcoming intermittency by adding storage, the net energy is reduced below the level required to sustain our present civilization.

BNC Postscript

When this article was published in CiA some readers had difficulty with the idea of a minimum societal EROI. Why can’t we make do with any positive energy surplus, if we just build more plant? Hall4 breaks it down with the example of oil:

Think of a society dependent upon one resource: its domestic oil. If the EROI for this oil was 1.1:1 then one could pump the oil out of the ground and look at it. If it were 1.2:1 you could also refine it and look at it, 1.3:1 also distribute it to where you want to use it but all you could do is look at it. Hall et al. 2008 examined the EROI required to actually run a truck and found that if the energy included was enough to build and maintain the truck and the roads and bridges required to use it, one would need at least a 3:1 EROI at the wellhead.

Now if you wanted to put something in the truck, say some grain, and deliver it, that would require an EROI of, say, 5:1 to grow the grain. If you wanted to include depreciation on the oil field worker, the refinery worker, the truck driver and the farmer you would need an EROI of say 7 or 8:1 to support their families. If the children were to be educated you would need perhaps 9 or 10:1, have health care 12:1, have arts in their life maybe 14:1, and so on. Obviously to have a modern civilization one needs not simply surplus energy but lots of it, and that requires either a high EROI or a massive source of moderate EROI fuels.

The point is illustrated in the EROI pyramid.4 (The blue values are published values: the yellow values are increasingly speculative.)

Finally, if you are interested in pumped hydro storage, a previous Brave New Climate article by Peter Lang covers the topic in detail, and the comment stream is an amazing resource on the operational characteristics and limits of this means of energy storage.

Besides the different materials that we can use for the different methods of producing energies, I do hope that at theend of the day, poeople actually do need to buy these electricity storage solutions and the storage prices have got to be at the very least competitive. If what we're trying to do is really revolutionalise the way that we consume resources in this world, then we're really not doing enough at this moment to put all the solutions into an actual marketable solution for everyone.

This German simulation study shows the results of four different scenarios with variables; storage*), flexible load, different mix's of solar & wind with increasing shares of those in electricity production.The study shows that with flexible power plants (so after 2023 when all nuclear is gone), the losses & cost due to storage will be minimal even while the share of wind and solar is 35% - 50%.

Restrictions of the simulation study, such as no im- and exports, imply that in reality results with high shares of wind & solar will be far better. Especially since Germany's interconnection capacities to the Nordic and the alpine countries are expected to be increased. E.g. Netherlands is implementing two new high capacity interconnections, so NL can trade more electricity.

Hence little losses & costs to be expected until wind & solar have a share >70% in the electricity generation.

___*) I assume that 40GWh storage with a capacity of 9GW was chosen, because the ~35 existing pumped storage facilities in Germany have similar capacity.

Most of the comment threads below have drifted considerably away from the thesis of the article -- that when sufficient energy storage for buffering the intermittency of renewables is added to the system, its net EROI becomes too low for economic viability. It's an interesting thesis. I don't entirely buy it, but I wish that more of the comments had addressed it.

I've never been a big fan of EROI analysis. I don't fault its good intentions, but it pretends to a fundamental validity that I don't think is warranted in practice. For one, there's the "boundary problem". How does one decide where to draw the line for what you count as "energy in"? A classic example is "the kids' soccer practice". If someone is employed in the nuclear industry, should the gasoline used to drive their kids to soccer practice count as "energy in" for nuclear power? The methedologies for some analyses have implicitly said "yes". That's how one manages to get the EROI number for nuclear power to come out low. The rules for drawing boundaries are inherently fuzzy, and can easily be warped to suit the analyst's agenda.

That's not to disparage the honest work of professor's Weissbach, Hall, et. al. They are trying to get at something that is genuinely important. But even the most rigorous of analyses are forced to resort to an artificial "cost to energy" equivalence ratio for estimating energy in. There is, for any nation, an overall ratio of GDP to energy consumption that is easy to find. When the actual energy inputs needed to produce some particular component of a system are too diffuse and difficult to identify, the fallback is use its cost as a proxy for its energy in.

That may be the only reasonable option, but it can't account for factors that cause wide variations on the actual cost to energy ratio for real components. What's the "energy in" to produce an aspirin pill, for example. If the pill comes from a bulk purchase from a pharmaceutical supplier, its cost will be a fraction of a cent. If it was administered in hospital, its cost might be $10. So what's "the" energy cost to produce an aspirin pill? On the basis of a cost to energy equivalence ratio, the answer will differ by three orders of magnitude depending on what cost is chosen.

In the end, it seems to me that EROI analysis is simply an economic analysis denominated in joules rather than dollars (or pounds or whatever). It's obviously true that an energy system must produce a healthy surplus of usable energy over and above its input requirements in order to be sustainable. However, stating that its EROI must be greater than some specific over-unity value is really a statement about the fraction of GDP that the analyst believes we can devote to energy without major impact to the economy. It may be accurate, but it's not fundamental. Economies do reshape themselves in major ways over time.

My understanding is that the higher the EROEI, the lower the ESOI necessary. If we power a world on solar which is estimated to have eroei of 7, and if we need to store the inverse of its capacity factor in a medium that gets less than .5 (say, ammonia), then overall net energy to society would either be impossible or require such vast amounts of land to make it almost impossible. If we stored it in batteries that get an ESOI of say, 10, then we can net a lot more energy with less land covered. And with pumped hydro, better yet.

If we use advanced nuclear, then we can obviously afford the low ESOI of ammonia, especially since it has a much higher capacity factor.

Brilliantly written, Roger. Your final three sentences have the crux of it:

"However, stating that its EROI must be greater than some specific over-unity value is really a statement about the fraction of GDP that the analyst believes we can devote to energy without major impact to the economy. It may be accurate, but it's not fundamental. Economies do reshape themselves in major ways over time."

On the question of storage and whether "buffering" really reduces EROEI by the amounts seen; the answer is that of course storage loses some energy, but only some of the energy buffered, and only a fraction of the power generated needs to be. Most of it can be utilised concurrent with generation.

Curtailment of excess generation for a limited number of hours each year is almost entirely free of costs (even if it does reduce the EROEI figure somewhat over that theoretically achievable, it doesn't change the economics of operating the system for the remainder of its potential generation which can be actualised). Demand management and time-of-use pricing, already in widespread use to smooth out diurnal demand variation and to shave demand peaks, can and does time-shift demand without the use of storage.

EROEI measures completely overlook arbitrage and opportunity costs.

All power storage technologies are lossy. You get less energy out than you put in. But this is not a problem for any other mechanism we have which converts or transports energy from one form or place to another, be it a power station, an oil tanker, a transmission line, or a vehicle transmission. We are purely and simply prepared to pay more for energy in the form of forward motion than we are for energy in the form of coal. Likewise, we are prepared to pay more for electric power in the hours of peak demand than we are at 2am. On-grid power storage is arbitrage, buying energy when it's cheap and selling (less) energy when it's more expensive. It is worthwhile if that arbitrage pays for itself, regardless of how lossy it is. A lot of existing grid power storage very clearly already does already pay for itself, so I can see no obstacles to expansion of the storage market as the technology develops, especially but not exclusively if the demand for storage is driven up by intermittent generation becoming dominant.

By the way I think that you are actually far too kind to Weissbach and Hall. Their analysis of solar energy in Spain incorporates dollar-priced inputs which are decidedly not in the form of available, high-value industrial energy such as electricity or gasoline -- namely land acquisition and leasing, administrative costs and the like -- and converts them into an energy equivalent. By extrapolating W&H's reasoning only a little further, all of society is part of the energy system, 100% of employment and investment are part of the energy industry, we have an overall EROEI of 1:1. This is obviously the case no matter what energy technologies society is using, no matter how much energy is in use, no matter how efficiently it is used or how sustainably it is produced. Decisions about energy systems are not based on EROEI numbers, no matter how widely or how precisely the net is drawn, but on social preferences and currency-denominated competitive costs (*including* societal choices to subsidise or socialise costs or benefits).

With hydrocarbons, the end result will obviously be less than 1 unless we use them to develop a source that has more global potential and which has a high enough eroei (and a high enough capacity factor) to deal with whatever low EROI which best fits convenience.

Costs, time value of money, externalities, and human desired results are what count. For instance, EROI is a phony measure taken from ecosystem analysis where the main energy is food. Nuclear, coal, biological, NG, money play no part in natural ecosystems.

Consider time value, an animal that lives 2 years doesn't care about electrical energy 40 years from now, todays food is what it is all about. Todays food is infinitely more significant than a KwHr in 1 or 5 or 10 or 20 to 40 years.

Of course, the utility guys would like to pretend time value of results and externalities are zero and don't count, so they are latching onto this nuts ecosystem miss-applied measure of success. Pure irony is, they have near no clue about ecosystems or living innovative things.

Cost and financial measures for a human relevant time frame(10 to 20 Yrs) are the most apropos measure of success, obviously. Real people are making generally wise financial energy decisions, IMO.

I find the argument for energy storage rather repetitive. Everyone agrees that it's important for it to happen before we can move forward, but so little people are being involed in the innovation and production of viable options for energy storage! I mean I'm getting flustered because there seems to be so much benefit in doing so, but discussions and talks only, and no action.. When can we really see a real break through?

One of the misconceptions about energy storage is the total conversion losses.

It is possible with Solar thermal to directly store heat energy and with Wind and Wave to directly produce compressed air instaed of electricity.

Compressed air is a dispatchable potential energy that can be used for electricity generation on demand.

By using these renewable sources to store energy directly instead of into electricity then storing surplus electricity by converting them in some other way makes them much more efficient.

The total useable energy is increased in this way, in the case of compressed air it can also be transported by pipeline (additional storage capacity) and can be converted to electricity onsite on demand.

It can even be used for transportation uses on a campuses, airports or military bases.

Grid energy storage is not necessary with the right generation mix and with enough dispatchable load. And the ultimate dispatchable load is fuel synthesis, since the market for direct fuel use is about double the size of the electric power industry.

The best kept secret in the energy industry is that ammonia can be used as a fuel for transportation or stationary power, in just about any application that uses gasoline or diesel. And ammonia is the cheapest fuel which can be made from solar, wind, or nuclear energy (the only other ingredients are water and air).

This link describes a recent conference on ammonia fuel. There are several demonstration programs going on around the world. The only thing missing is public awareness (i.e. it is not being promoted by any of the big energy companies).

Batteries are made to store short term for a limited cycle energy and they are very economically for many such uses. In other words, storing energy for a day or a few days is a good cost effective use vs not being smart and trying to store energy for a year would not be smart.

Simple logic and physics tells you that there will be no storage of electricity for low value bulk needs. How can a battery compete with a million ton pile of coal on the ground which is effectively storage at a cost of very close to $0/kwh

Thermal storage (CSP or Nuclear) is also extremely difficult cost wise but maybe it can get towards GWh storage scales at costs of $1/kwh which might just about work as they can sell at higher prices and storr during low prices directly using heat

Also you can guess the lower limit of storage prices. If a battery was made of pure aluminium it wpuld cost $10/kwh. If it was made of a semi finished aluminium product it woupd cost $50/kwh. Why aluminium? Aluminium is dirt refined into something use able. The second most produced dirt to metal product. So I wouldn't hold my breath for batteries below $50/KWh and certainly not below $10/kwh both of which are too expensive

In response to Roger Rabbit: Replacing oil will require a multi-terawatt installation, no matter which combination of energy source and energy carrier is chosen. An energy carrier cannot be made without putting the energy into it first, and there is no way around that. Of course, there are other schemes, but we know how to classify those. The estimate of electric power for battery/electric sounds about right, but it doesn't take into account the transmission losses on the grid, battery charge/discharge losses, or the cost of making the battery itself. Energy used for making ammonia would be purchased at or within the plant, whereas electricity for charging batteries would be purchased at a higher post-distribution price from the grid. Also, a combination of heat and electricity can be obtained at the plant, but not from the grid. Generation efficiency from reactor heat to ammonia is something like 48% on a higher heating value basis, or 40% on a lower heating value basis, and an engine optimized for ammonia/hydrogen will have an efficiency of something like 40-50%. Diesel engines routinely run at about 40% thermal efficiency. 15-20% plant-to-wheels efficiency for nuclear/ammonia/IC engine appears doable.

For more information see:Nuclear-Power Ammonia Production by William KubicUS Patent No. 8,813,691

Even if using electricity is more efficient than making ammonia and burning that, the ammonia pathway may be cheaper. For a range comparable to that already obtained with gasoline, a battery roughly doubles the weight of the car, and the ongoing battery replacement cost also heavily affects the overall economics of using batteries. "Even if the electricity were free..." The market will eventually sort this.

Personally I think ammonia is an absurd proposition. Why would you do nuclear electricity (or wind) to ammonia to internal combustion engineto kinetic energy. By your own admission the electricity to movement efficency is only on the order of 15%...20% tops.

Compare that to direct overhead line at electricity to motion efficency of 95%.

So if you need 1,000 nuclear reactors for the ammonia idea well you would only need about 150 for the direct electricity idea

Also nuclear at $5cent to ammonia at $20 cent makes no sense when you could just use bio diesel at $10 cents

Ammonia really is silly in every ppossible way and it isn't going to happen. Both nuclear and wind proponents like it as it potentially helps their arguments in trying to convince themselves a 100% nuclear or wind world is possible. However reality and math simply says no no no and no to ammonia from electricity

If I give the motor controller an efficiency of 90%, and count the energy used for making the battery (ESOI = 10) by tacking on another 90%, the total efficiency of the battery/electric system drops to 0.33 x 0.9^5 = 0.195 = 19.5% which is actually lower than my upper figure of 20% for the ammonia/engine system.

The ammonia system can be made that efficient only if direct heating is used for making the ammonia, such as the case of using a thermochemical cycle to make the hydrogen, or if the hydrogen is made in a system that takes heat as a substantial input, as in the case of high temperature steam electrolysis.

Ammonia cannot be made at 40% conversion efficiency in a system that uses electricity/electrolysis without substantial direct heating. Generation of electricity followed by making hydrogen from the electricity by low temperature electrolysis is very inefficient, something less than 20%.

Actually, electricity is not 95% efficient. The present generating efficiency of the power plants + grid losses is about 33%. Let's give the battery charger an efficiency of 90%, battery charge/discharge efficiency of 90%, and the electric motor an efficiency of 90%. The plant-to-wheels efficiency of battery/electric is thus 0.33 x 0.90 x 0.90 x 0.90 = 24%, which is slightly higher than my upper figure of 20%. It's only a factor of 1.2, which isn't enough to decisively favor battery/electric over ammonia/IC engine, especially when other factor like range, battery weight, and battery cost are considered. It's the difference between 1000 and 1200 power plants, for example. The market will seek to minimize total cost, which may not correspond to highest efficiency.

Ammonia is not an absurd proposition. There is and will continue to be a need for fuels with much higher energy densities than batteries will ever be able to deliver. Air transport is an obvious case. Ammonia is not a great fuel for such applications, but it's easy to make and generally adequate. It's particularly good as a store for hydrogen, in applications that employ high temperature fuel cells for portable electricity.

The interesting question for me is whether the comparative easy of synthesis of ammonia is enough to outweigh its lower energy density, compared to synthetic gasoline and diesel. But addressing that is a deep dive into details of reaction kinetics and process yields, in a dynamically evolving world of chemical process technology. Way above my pay grade. I'm happy to let industry sort that one out.

I advocate starting to move forward today with ammonia fuel, knowing full well that the transition to non-fossil energy will take many decades. In particular, I expect we (in the developed world) will be using fossil-derived transportation fuels long after we stop using fossil fuel for electricity (renewable and nuclear electricity is rather low hanging clean-energy fruit).

So in this syn-fuel future, with no fossil fuel used for electricity, from where is the CO2 for synthetic gasoline going to come?

As of today, direct air capture of CO2 will make syn-gasoline hopelessly uncompetitive with ammonia. I realize that not everyone will want ammonia in their cars, but for those people, battery electrics are available. We've discussed sea-based CO2 capture on TEC before, but I thinks that only works for mobile systems like OTEC and aircraft carriers, due to poor mixing.

"So in this syn-fuel future, with no fossil fuel used for electricity, from where is the CO2 for synthetic gasoline going to come?"

Two obvious and easy sources: (1) cement production, and (2) biomass. Biomass itself can be used in a couple of ways. One is fermentation to produce alcohols, followed by capture and utilization of the CO2 stream from fermentation. Roughly doubles the liquid fuel yield per ton of biomass. The other is low temperature pyrolysis to produce syngas, condensible liquids, and biochar. Fuel yield per ton won't be as high as the first approach, but the biochar, used as a soil ammendment, sequesters carbon and enhances soil fertility.

The amound of liquid fuels produced by these means won't be large compared to current production of petroleum-based liquids, but it won't need to be. Batteries, direct electrfication, and a diminished need for personal transportation due to increasing role of VR-based telecommuting and home shopping (the latter aided by efficient semi-autonomous delivery services) -- all that will substantially reduce the need for liquid fuels.

Reduced demand for liquid fuels will probably become economically significant even before oil production declines sharply. Also, it's not an either/or choice between ammonia and carbon-based synfuels that we'll be looking at. They will co-exist and compete for market.

I suspect that ammonia will find its most secure niche as a hydrogen source for FCEV's, in competition with batteries more than with carbon-based synfuels. The latter will be important for aviation and in competition with oil for the legacy vehicle fleet.

Indeed. "Carbon-negative" hydrogen production is an intriguing concept. It's very promising, but it needs funding to move it beyond its current status as a laboratory curiosity toward something that might prove economically viable.

So far, professor Rau hasn't had much luck in obtaining funding. It's too much "applied R&D" for the NSF and academic science organizations, and too "academic" to attract attract venture funding. This country really needs a mechanism to address that class of development.

There are non-fossil CO₂ point sources aplenty in the world, including biogas digesters, sewage, and geothermal volcanic vents such as the one being used by Carbon Recycling International as the carbon source for the synthesis of methanol.

The US Navy's synthetic fuel research project determined that the space and energy requirements of air capture were excessive, and they came up with a clever method ("electrochemical acidification") to obtain the CO₂ and some of the required H₂ from the dissolved carbonate and bicarbonate salts in seawater. The energy spent is mostly recovered in the form of hydrogen, with a potentially high-value alkaline hydroxide byproduct as well. (Alternatively the hydroxide stream can be diluted back into the ocean where it can additionally help reduce the harmful ocean acidification caused by carbon dioxide pollution).

The biggest problem with battery electric vehicles is that personal cars do so few miles that the fuel price savings isn't worth the additional capital cost.

Two ways around that. One is for the price differential between battery and petrol cars to fall. We both probably think that unlikely.

The alternative is that the battery vehicles do many many more miles in their say 15 year life. Currently with a personal car doing 10k miles a year or 150k miles over its life the battery vehicles are nit viable but what if a car did 3 million miles in its life? the cost of the battery system per mile falls to 1/20th which would probably make it viable.

And of course all the material or production limits also fall by 1/20th

There are currently vehicles which do do many more miles than personal cars eg HGVs / Buses / Trains so maybe they can be converted to batteryt operation. They should probably be the focus at this point. In the future self drive taxis will also have bery high mileage per car and could make battery tech viable where it currently isn't

But long-cycle-life batteries don't exist yet for cars (in deep cycle). The high temperature sodium-sulfur (liquid metal) batteries are claimed to have 20 year lifetimes with daily cycling, but these are unsuitable for cars. Li-ion researchers have claimed long cycle life for laboratory samples, but the batteries on the market today are only good for a few thousand cycles (Tesla's entry level model has a 125,000 mile battery warranty).

Of course shallow-cycling extends cycle life, but that doesn't fix the economics, since it makes the battery more expensive for a given daily mileage. Also, it makes the vehicle heavier and less energy efficient.

I know its > 1000 as I have had mobiles I've deep discharged and charged back up that many times.

I think at this stage the number of cycles is more important than the number of years. For instance a HGV might do 1 million miles in 3 years.

With a 500kwh battery it might get 300 miles. So if it can cycle 3500x it will allow 1 million miles. At which point maybe you can buy a replacement battery rather than replace the whole truck. Also maybe replacement electric wheel motors if required (but they should have 5m miles lives). Alternatively if the batteries still function ok after 3500 cycles but the capacity has dropped to say 200kwh from 300kwh maybe you cpuld just add a new 100kwh battery to make up thr lost capacity.

Overall my point is there are two ways to make battery vehicles more realistic. First is for the battery vehicles price premium to fall and second is for the number of miles used to go up. Fortunately there are vehicles that already do lots and lots of miles. HGVs and buses which should be more viable for conversion than cars

For each 100,000 miles an EV does compares to a 45mpg oil car with 13 cent electricity and $3.20 per gallon petrol

The cost is roughly $4k electricity vs $7k petrol or $3k fuel saving per 100,000 miles

Clearly a typical car doing 100k-150k miles in its life isn't going to pah back. But a car doing 1 million miles will save $30k in fuel costs and probably an amount in maintenance and replacement parts too.

So its a matter of lifetime range. Buses and HGVs could be used for 2m plus miles. You would however need li-ion batteries capable of doing 5000+ cycles whole retaining 2/3rds of capacity.

Also the saving is about 2/3rds off the trade balance. Ie les money escaping the country to fund arab kings buying $150m warplanes

Another throwaway line we keep seeing says something about the grid being problematic, too old, etc., like this one:

"the U.S. electric grid is a sprawling system that represents one of the greatest engineering achievements of the 20th century. Yet, after decades of ostensible neglect, it is showing its age, worrying experts and policymakers alike."

Umm, so what? The real problem with the grid, if any, is that in some places the people don't have one.

The obvious solution is that more people need power generation and they need to get a grid. However, there is nothing inventive about saying that. It seems the obvious answers leave our reporters and academics with little to do.

After reading through a lot of the comments here I feel rather disheartened by the amount of conditions that need to be satisfied in order for us to have a good lef into the whole sustainable energy - energy storage conundrum. What we can hope for here is that with all the brilliant minds, we're able to do the best with what we have and continue to improve. I really have to agree with @Muriel Strand here and say, how much energy do we really need to live a satisfactory life?!

This is all good, but the diagram with all the energy balls misses a key point -- Thorium is 4x as abundant as Uranium and is indeed a path for advanced nuclear designs, as the Indians are already doing, and as the Chinese are now developing...

Furthermore, the Uranium ball in the diagram may only be considering U235 fission, which is only 0.7% of total natural Uranium. So the actual fission energy available from Uranium and Thorium, bred in reactor to U233 and Pu239, is truly vast. Just our existing ~70,000 tons of 'spent' LWR fuel is sufficient to power the planet for hundreds of years, via breeder reactors, like IFR, MSFR. Add in the even greater mass of U238 enrichment waste, and...well, look at folks like Terrestrial energy Inc.

Thorium, by the way, is a waste product of rare-earth mining, and one typical RE mine piles up ~5000 tons of Th each year -- enough to run the entire energy needs of the planet for that year. Mars & Moon, etc. have abundant Th as well, if anyone wants to go there and needs local powe. ;]

There is not now, nor will there ever be a shortage of sustainable energy resources. As long as there are customers will to buy $4/gallon-equiv fuel, industry will build the facilities needed to make it.

* the graphic ignores all of the thorium and 99.999% of the uranium in the world (ideological bias).

Consider contacting Richard Perez. He is a busy guy but accessible. Mention your thoughts about the bias of the graphic and see what he says. He is easy to find with a few minutes of Google time. Last time I went looking for him he had a web page that was reasonable inviting and did not occur to me as a firewall.

He has always been a strong advocate for solar energy but also is respected and seems to strive to be objective.

Presumably the anti-nuclear bias in the graphic results from Perez's own bias (i.e. his comparison assumes nuclear power which is limited to the most common and most economical form, but uses a solar interpretation that assumes future breakthroughs in storage and economics). My goal is not make everyone share my biases, but rather to simply insure both sides of the issue are available for seekers.

The reason I suggested you contact him is so that you don't have to presume.

Richard was promoting solar at a time when he was in the vast minority. He has worked hard to use the system to monetize those benefits that the current system ignors. What looked like overzealous idealism a decade ago now looks like wisedom in hindsight. He may benfit from your insights on nuclear power. You many benefit by learning why he is not sharing your perspective on nuclear power.

Whether I agree with the conclusions that are to be drawn from his work or not, I rarely go away without finding value and the efforts of a well thought out position.

Anyway, if you don't, I may have time in December as I am a bit curious myself.

Why do I predict that in the future, people will prefer cars with internal energy storage rather than powered from overhead wires? Because internal storage is what the vast majority of people have used in the past, and continue to choose today. There are plenty of trolley and bus systems around to demonstrate the concept; there is no market for cars powered in this way.

If you look at the cost of fuel in places like American and the UK, the cost range is huge. I can only conclude that the cost of fuel doesn't matter, people love cars with internal energy storage.

People used to prefer horses mules and donkeys once upon a time too......

Ammonia is too energy inefficient to work. Even high cycle battery EVs are more plausible than ammonia especially for high utilisation vehicles like HGVs Buses Trains

Also I've suggested to you previously. What advantage does ammonia have over biofuel which can and already is produced at a cost in the region of sub $10cent/kwh

Its more viable as you don't need to sink trillions into ammonia plants and nuclear stations (which require a tremendous upfront cost and any future shift which nakes ammonia powered travel less desirable would result in trillions lost)

Nuclear can be used for electricity generation there is no need to use biofuel for electricity generation.

I wss saying using nuvlearr to make ammonia and to then burn that in a piston engine is not likely and offers not a lot over biofuel in cars but has many many negatives.

As for biofuels can't scale I don't buy that argument. With computer driven vehicles the energy demand for land travel will be cut even for a world.of 8B developed. I would imagine only in the region of 1-2TW of biofuel would be required.

The world currently grows about 2TW of bio energy (aka food) so it would mean 50-100% expansion in farmed land (less as productivity tons per hector are increasing) which doesn't seem implausible.

Battery electric vehicles make no sense for personal cars but could work for HGVs/Trains/Buses as in a year they drive 20x as many miles so payback on investment is 20x quicker. Computer cars complicate things a but further.

I can see potentially computer controlled battery cars as viable. Imagine a battery fleet of self drive taxis in cities. They vould do 500 miles a day and would be far more efficient than petrol or diesel cars in cities. Charging would be much less of an issue the fleet can just go to certain points in the city for a quick charge or battery swap. Loger distance travel could be done by normal cars powered by biofuel.

Whatever the case the much higher utilisation of computer controlled vehicles makes the economic case for a higher upfront cost but lower running costs more vuable than a human personal car doing just 8,000 miles a year.

I like the idea of super efficient (auto)mobiles and realize that we humans are very inefficient when it comes to having to waste all that momentum, having to stop all the time, and "inchworming", not knowing how to conserve momentum, etc.

I'm just afraid of computer crashes due to animals and unexpected events. I better like the idea of personal rapid transit. At least, there would be less stops (or crashes) due to such events. And, I believe, they could be safely electrified ditching the need to carry fuel altogether!

It could be used to fill in for load following rather than building extra pumped hydro or molten salt storage. If solar really kicks butt, then nuclear would have to make large amounts of it in the day, just to keep operating and to prevent even more fossil fuels combustion at night. It would seem that there would be extra to sell to the liquid fuels market. Also, that infrastructure would "set in" as CO2 restraints increase, to power much of the remaining non battery machines.

I agree, it would be far more efficient in the long run to design "everything" to run on batteries, however, a source such as advanced nuclear can "afford" quite a bit of inefficiency. It might even compete directly with propane and future natural gas.

If the purpose of switching away from fossil fuels is to avoid greenhouse gas emissions, switching *to* ammonia with the purpose of burning it seems folly to me. Burning ammonia produces various oxides of nitrogen, including N₂O which is a significantly more powerful greenhouse gas than carbon dioxide.

I'm far more convinced by the projects which are already under way in the energy industry for storage of excess clean electric energy and/or conversion of fossil energy into more useful forms.

For simple stationary storage of electricity, in addition to batteries and traditional pumped storage, compressed air storage and cryogenic or pumped heat storage are in active development and could in the long run realise costs well below pumped hydro, due to their much more flexible siting and scalability.

For transportation or long-term (seasonal) storage of excess energy, synthetic fuels would seem to make a lot of sense. Ammonia is one, but it is not as far as I am aware in practical use as a combustion fuel today.

Several other synthetic fuels already are. These include straight hydrogen (pure, or for admixture into the natural gas supply), synthetic methane (for the gas grid ditto, or for CNG vehicles), synthetic methanol or MTBE (liquid fuel), and synthetic hydrocarbons from Fischer-Tropsch synthesis (already in large-scale production in coal-to-liquid and gas-to-liquid plants; excess clean electricity could also be a viable energy source) or via methanol using the Mobil process.

Most of the reasons we already find carbon-based fuels more useful as energy carriers than ammonia or pure hydrogen will still apply when the energy source for their manufacture is not fossil fuel but clean electricity.

It is true that burning ammonia produces more nitrogen oxides than gasoline, but it is also true that having small amounts of ammonia in the catalytic converter allows more effective cleanup of the exhaust (some power plants use this trick today - see SCR). As a result, mass market ammonia fuel vehicles will meet the same exhaust standards as today's cars, with no CO2, sulphur, or particulates.

Saying we should ignore a proven (bird in the hand) technology like ammonia fuel, in the hopes that a breakthrough in some other area (CAES, pumped hydro or whatever) strikes me as a bad idea.

The other syn fuels that are in use today are just distractions and ways to prolong the use of fossil fuel (often coal, the dirtiest of fuels). We'll phase out fossil fuels first in electric power, and later in transportation fuel. So by the time synfuel made from renewable and nuclear power becomes big, there won't be much CO2 available for making hydrocarbon synfuel (direct air capture is CO2 is expensive, uses a lot of water and land). We can get enough CO2 from cement making to fly our airplanes, but not much more.

Sure hydrogen synfuel will have a market. It is great for baseload applications like steelmaking, when produced from a baseload source like nuclear. But with excess spring/fall windpower and summer solar, we'll need seasonal energy storage, which can only be done with liquid fuel, such as ammonia.

Ammonia is a much better car fuel than hydrogen also, with double the energy density of 10,000 psi H2, and 30% better than CNG (GNC is near the pain threshold, so H2 has a big problem). Ammonia is a clean fuel when used in fuel cells or piston engines; it's cleaner in piston engines than hydrogen too, because H2 burns hotter, making more nitrogen oxides.

I agree that hydrocarbons are better automotive fuels than ammonia, but only slightly better. We can make the compromise to get the environmental, climate, and energy security benefits (in fossil fuel importing countries it could be cheaper too).

I would think it's easier to make ammonia than carbon based fuels from clean sources of heat and electricity. I believe there are ways to extract the energy from it without emitting much N2O. The main components is water, not the greenhouse gas, thus should be much less of a problem.

Nevertheless, I agree that the production methods of the other forms of storage should be developed to reduce costs. Batteries require a 2 dimensional boundary which increase costs compared to the volume of heat and gravity storage. This is one reason why I believe there will be no mainstream utility scale battery storage except as a bridge for whatever small amount of time needed to utilize the other storage sources.